And that's irrespective of region? So in the US merino leather is not a "regular" option (i.e. you can't use the standard builder to add it), so it's at a special request.

I suppose the bigger issue is the pricing, since it's not subsidized in the 3 series for the US market as it is in other models that do offer it (i.e. 5 series)

Yes that's right, that rule applies for any region. HOWEVER, getting approval for Merino in a G20 in the US would require some element of approvals by BMW NA which could push it out your build slot. But that's not due to the option itself but the approval process dragging it out.

As you know, when the dealer builds a car right off the local-spec option list, they can just pop in the relevant codes against a car already in their allocation (provided it hasn't started production) and they could effectively have a car being made to your specification within a few weeks + shipping. But since you want a non-US spec option, that'll have to go via the BMW head office to get approval (which presumably isn't too quick) before they can add the option in - and I think only an administrative user can add non-local spec options to the car even after this approval has been granted. I think there's only one person in a dealer who has this access and it's a collaborative exercise with the head office to do. It really shouldn't be hard or slow but hey big business slowness is common in all industries .

So you just need to work with the dealer to get that approval and then afterwards those more 'regular' merino options are all yours ASAP (but for a pretty $$$$ price). My M340i order (Australian), was placed in mid-December and accepted for a Week 3 Jan 2020 build allocation per my request (calendar year is important in our part of the world for resale so i wanted one of the first 2020 slots) with Full Ivory Merino.